Post-Apocalypse

Ida was presumably in the crowd witnessing the death of either Ava or Tripp at the order of Joan. As the firefight breaks out and zombies enter Richmond through the hole in the wall accidentally made by Kate, the walkers attacked and devoured Ida, horrifying her mother.

Death

Killed By

Since the hole was created when an unnamed new frontier soldier threw a molotov at the truck Kate was driving, this resulted in her crashing into the wall, therefore letting the walkers in. Ida's fate was confirmed by her mother, Fern.